Medical headlamps include a carrier frame or a headband, with which an illumination unit can be carried on the user's head, as well as the illumination unit itself, which is carried above the user's eyes. The illumination unit can include a light source or an optic fiber by which the light generated from an external light source is transmitted into the illumination unit. The illumination unit comprises an illuminating lens through which the illuminating light generated from the light source or transmitted by the optic fiber is projected onto an object, such as onto a tissue surface, to illuminate an object field required for a medical investigation or for a surgical intervention. A medical headlamp can also be equipped with a viewing aid, such as binocular lenses, or else with a head-borne video camera.
In a medical investigation or a surgical intervention, it is desirable that the investigative or surgical site should be illuminated as homogeneously as possible with a strong light intensity sufficient for recognizing all details. The illuminated object area should be delineated with the sharpest possible edges so that as little illuminating light as possible is lost by illuminating areas outside the investigative or surgical site; in addition, thanks to sharply outlined demarcation of the illuminated object area, the entire heat development as well as the risk of glare affecting other persons is reduced.
In addition it can be necessary to illuminate object areas of various sizes and/or object areas in different working conditions. If the illuminating lens generates an illuminating bundle with a large opening angle, then a large object area can be illuminated. On the other hand, the light intensity can then be insufficient for recognizing details, especially at a relatively large working distance. If, on the other hand, the opening angle is small, then no doubt a sufficient illuminating intensity can still be achieved even at a fairly large working distance. In particular at a small working distance, the illuminated object area can, however, be too small for the intended investigation or operation. A sharp-edged delineation of the illuminated object area is desirable in each case, even at varying working distances.
Headlamps have therefore been developed that make it possible to modify the light distribution of a generated illuminating light bundle.
According to U.S. Pat. No. 5,430,620, a lens is placed before the outlet surface of an optic fiber, said lens being movable along the optical axis of the end portion of the optic fiber by means of a screw thread, so that the distance between the lens and the outlet surface of the optic fiber can be modified. This allows an adjustment of the size and brightness of the illuminated object area to the respective requirements, such that the outlet surface of the optic fiber is sharply configured only in the position of the greatest distance of the lens from the light-conducting surface. U.S. Pat. No. 7,314,300 B1 discloses a multi-lens illuminating lens system of a surgical headlamp in which the distance between a light-conducting surface and a convex lens can be modified by sliding a light-conducting attachment. This enables the light distribution in an illuminated object area to be modified. An adjustment to different working distances is not likewise foreseen as a result.
DE 32 11 187 A1 teaches how to axially slide a glass rod attached on a free end of a fiber optic light conductor, together with a diaphragm directly adjoining its light-radiating surface, with respect to a collector in order to sharply image the diaphragm into different working distances. As a result, an observation field situated in a pre-selectable plane can in each case be illuminated with sharp edges. The collector here can be configured as a vario system; such a system includes a number of lenses, which are slid with respect to one another, and it involves high manufacturing and adjustment expenditure.
Familiar from the prior art, the modification of the light distribution of an illuminating light bundle by mechanical adjustment of one or more lenses or of a light-conducting end causes an increased insulating expenditure because of the cleaning and sterilization requirements applicable in the medical field; this is especially true when the illuminating lens is part of a medical headlamp or is positioned in the distal end area of an endoscope or exoscope. An exoscope is understood to mean an observation device that is intended for use outside a cavity, such as is described in DE 10 2011 001 200 A1. Both an endoscope and an exoscope can include an illuminating lens to generate an illuminating light bundle, or a separate illumination unit with such an illuminating lens can be associated with an endoscope or an exoscope.
The aforementioned solutions for modifying the light distribution also result in an enlargement of the structural size and weight of the illumination unit, which is also not desired. Illuminating lenses, in which only one lens can be moved or one optic fiber end can be displaced with respect to a fixed lens arrangement, allow no independent adjustment of a focus and of a size of an illuminated object area at various working distances.